Making peace with the fact that I'm way too stupid to write bug free code.
This leads to a surprisingly large number of practical habits.
1. I welcome code reviews. Some people can't stand their code being criticized by other people. To me the fact that someone else spends time improving my code is a clear win. Ego is not bruised if you start with assumption of being stupid.
2. I seek out and use tools that help me find bugs automatically and understand my code better. Static code checkers like clang analyzer or cppcheck or pychecker or lint. Valgrind, good memory and cpu profilers, good debuggers. Source Insight (an editor).
3. I see enormous value in continuous build systems and automated testing (be it unit tests or more holistic tests).
4. I step through new code I write in the debugger just to verify that it behaves the way I expect.
5. I stay away from complexity, both self-inflicted (like trying to be too clever when implementing something) or inflicted by the tool (e.g. I avoid using advanced features of C++). I avoid multi-threading as long as I can.
6. I add diagnostics to my code. Logging, asserts in debug builds, built-in crash dump submission to my site for analyzing crashes that happen in the wild.
7. I know that despite doing all I can to prevent it, the bugs will happen and will have to read my own code to fix them long after I wrote that code. Therefore I try to make the code as readable as possible for my future self. Balanced comments (not too much, not too little). No cryptic names for variables or functions. No long functions with complex logic. I take the time to make my code look consistent.
8. It's better if other people sweat writing and fixing bugs in their code than me in mine. I look for high quality, reputable components instead of re-inventing the wheel. I would much rather use SQLite than write my own persistence layer.